The present invention generally relates to embolic protection systems and more particularly pertains to emboli capturing devices for use in conjunction with devices for intravascularly treating stenosed blood vessels. The system allows a vascular site to be treated while embolic materials that are intentionally or accidentally dislodged by such treatment are collected and retrieved.
Blood vessels can become stenosed or completely occluded in a number of different ways. A stenosis may for example be formed by an atheroma which is typically a fatty, fibrous or hard and calcified substance that forms on the lumen walls of the blood vessel. Alternatively, the stenosis may be formed of thrombus material which is typically much softer than an artheroma but can nonetheless cause restricted blood flow in the lumen of the blood vessel. Thrombus formation can be particularly problematic in a saphenous vein graft as well as in carotid artery and intracranial vessel disease due to the potential for thromboembolic stroke.
A variety of intravascular procedures have been developed for restoring the patency of certain stenosed or occluded blood vessels. The device or devices that are employed for such treatment are introduced into the vasculature at a readily accessible location and advanced therethrough to the stenosed site. In balloon angioplasty, a balloon-tipped catheter is positioned within the stenosed region of the blood vessel where it is inflated to dilate the lumen. A stent may additionally be deployed in the dilated region in order to continue to support the walls of the blood vessel after the balloon has been deflated and removed. Alternatively, the obstructing plaque or thrombosis may be mechanically removed or ablated in an effort to restore patency.
One problem common to all of these techniques is the potential for the escape of portions of the plaque or thrombus, resulting in emboli being carried downstream to lodge elsewhere in the vascular system. Such emboli can be extremely dangerous to the patient, capable of causing severe impairment of the circulatory system. Depending on where the embolic material is released, a heart attack or stroke could result, or in the event peripheral circulation is severely compromised, the amputation of a limb may become necessary.
Previously suggested approaches for dealing with embolic debris or fragments have included cutting the debris into very small pieces of a size on the order of blood cells so as to preclude the formation of occlusions at downstream locations. Such technique does however have certain problems including for example the difficulty inherent in trying to control the size of the fragments that are severed. Additionally, since a thrombus is much softer than an atheroma, it tends to break up more easily when mechanically engaged by a cutting instrument, thus creating the risk of causing large fragments to become dislodged when the thrombus is mechanically engaged.
Suction techniques have also been employed in an effort to remove debris immediately after it has been severed or otherwise dislodged from the lumen walls. It is however necessary to pull quite a high vacuum in order to ensure removal of all of the pieces severed from a stenosis. When an excessively high vacuum is employed, the vasculature may be subject to collapse. On the other hand, if an insufficiently high vacuum is drawn, all of the debris that has been severed may not be removed.
As a further alternative for preventing dislodged plaque from posing an embolic risk, various embolic capturing devices have to date been developed. Such devices are deployed downstream of the stenotic site being treated and serve to filter or strain the blood of any embolic material that exceeds a certain minimum size. Upon completion of the treatment procedure, the capturing device is retracted to remove the captured embolic material from within the vasculature.
A difficulty inherent in the use of such devices is the limited amount of space that is available within the vasculature. The device must be dimensioned and configured to permit it to be introduced into the vasculature, maneuvered therethrough and positioned downstream of the treatment site. This may involve passage through significant convolutions at some distance from the initial point of introduction. Once in position, the device must be deployable to a sufficiently large cross-section to effectively strain substantially all of the blood passing therethrough without unacceptably reducing its flowrate. Additionally, the use or the presence of such device must not interfere with the treatment of the vasculature site, nor may the treating device interfere with the function of the embolic capture device.
Some of the heretofore known devices employ a guide wire based configuration wherein the embolic capture device is affixed to the distal end of a guide wire or guide wire-like element. Such approach either requires the guide wire element to actually function as the primary access guide wire or requires the capture device, including its deployment mechanism, to be dimensioned so as to be extendable through a catheter lumen. While the former approach enables the emboli capture device to be dimensioned much larger than what would be able to pass through a catheter lumen, the association of the capture device with the guide wire severely compromises the ultimate flexibility and maneuverability of the guide wire and thereby limits its ability to access hard to reach destinations. On the other hand, while the latter approach allows a primary access guide wire to be used to gain initial access whereby full advantage can be taken of such wire's flexibility and low profile, the initial access wire must subsequently be swapped for the embolic capture carrying wire. Such task can be rather time consuming and problematic. Moreover, because the embolic capture device carrying wire must be extended through the catheter lumen, its maximum cross section is severely limited. Its effectiveness to strain the blood is thereby limited as is its ability to retrieve the collected embolic material.
It would be most desirable for an embolic protection device to be sufficiently sized to be able to effectively strain the blood flowing therethrough without limiting blood flow and without requiring a change out with a guide wire. More particularly, it would be desirable for the emboli capturing device to be of an over-the-wire design of a configuration that would not to interfere with the treatment of the vessel upstream therefrom and wherein such treatment does not interfere with the function of the emboli capturing device.